1. Field of the Invention
The present invention relates generally to the construction of catheters having liquid-filled lumens. More particularly, the present invention relates to a catheter design and method for filling a sealed catheter lumen which minimize the retention of gas bubbles within the liquid-filled lumen.
Arteriosclerosis is a pandemic health problem which can cause myocardiol infarction (heart attack) and a variety of other circulatory diseases. Arteriosclerosis is characterized by vascular constrictions, generally referred to as stenoses, which result from the build-up of atheroma and plaque on the interior wall of the blood vessel. Initially, atheroma is soft and has a relatively low density. Over time, however, the atheroma calcifies into a hard plaque having a high density which can significantly occlude a blood vessel. Moreover, once plaque forms, platelets can aggregate on the diseased blood vessel wall, forming clot and thrombus which further occlude the lumen.
Over the past decade, numerous approaches for reducing and removing such vascular constrictions have been proposed, including balloon angioplasty where a balloon-tipped catheter is used to dilate a region of stenosis, atherectomy where a blade or cutting bit is used to sever and remove the obstruction, and laser angioplasty where laser energy is used to ablate at least a portion of the obstruction. Embolectomy is a surgical technique where a balloon-tipped catheter is surgically introduced to a blood vessel and used to draw stenotic material back to the surgical incision from where it is removed.
In performing such therapeutic techniques, a vascular catheter carrying an appropriate device at its distal end is percutaneously or surgically introduced to the blood vessel. The distal tip of the catheter is then guided to the region of stenosis while the surgeon follows its progress using a fluoroscope. Once in position, the therapeutic procedure is performed and the catheter is subsequently removed.
A major limitation on the performance of such procedures has been a lack of detailed visual information. Although fluoroscopy can generally reveal the position and extent of blockage, little information is provided on the nature of the stenotic material and the boundary location between the stenotic material and the blood vessel wall. Without such information, it is difficult to tailor the treatment protocol to the individual patient.
Thus, there exists a need for intravascular imaging systems which can provide detailed visual information on the nature and extent of the stenotic blockage. Such a system is disclosed in U.S. Pat. No. 4,794,931, the disclosure of which is incorporated herein by reference. The disclosed system provides internal viewing of the blood vessel wall, allowing the surgeon to closely observe the obstruction and select the most appropriate treatment modality. The viewing further allows the surgeon to direct the treatment to the particular site within the region of stenosis where it will be most effective. Finally, the surgeon can immediately review the results of the treatment, allowing assessment and an immediate determination of whether further treatment is appropriate.
The imaging system in the aforementioned patent application employs a vascular catheter having an ultrasonic transducer in its distal tip. When configured for imaging, the catheter tip will be sealed and filled with a liquid medium to provide for propagation of the ultrasonic signal. Normally, the tip will be filled through an axial lumen which extends to the distal tip. The sealed nature of the tip, however, makes it difficult to adequately flush the lumen and distal tip in order to substantially eliminate the presence of air bubbles. Even very small air bubbles which would present no danger of air embolism can significantly deteriorate propagation of an ultrasonic signal.
Thus, it would be desirable to provide catheter designs which allow for filling of the catheter without substantial retention of air bubbles. It would be particularly desirable to provide catheters and methods for filling catheters which allow for venting and flushing of the catheter lumen leading to the distal tip which houses the ultrasonic transducer.
2. Description of the Background Art
U.S. Pat. No. 4,638,805, describes a balloon dilation catheter, where the balloon terminates in a small-diameter passage at its distal end. The passage is sized to permit the venting of gases while substantially inhibiting the flow of liquids therethrough. Published European application, 234,951 is the equivalent of U.S Pat. No. 4,794,931 discussed above.